Apparatus for operating gas turbine engines

ABSTRACT

A method facilitates assembling a gas turbine engine assembly. The method comprises providing at least one propelling gas turbine engine that includes a core engine including at least one turbine, coupling an auxiliary engine to the propelling gas turbine engine such that during operation of the propelling gas turbine engine, such that at least a portion of the airflow entering the propelling gas turbine engine is extracted from the propelling gas and channeled to the auxiliary engine for generating power, and coupling a modulating valve in flow communication to the propelling gas turbine engine to control the flow of airflow from the propelling gas turbine engine to the auxiliary engine, wherein the modulating valve is selectively operable to control an extraction point of airflow from the propelling gas turbine engine.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/352,446 filed Jan. 28, 2003, now U.S. Pat. No. 6,968,674which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to the gas turbine engines, and, moreparticularly, to methods and apparatus for operating gas turbine enginesused for aircraft propulsion and auxiliary power.

Gas turbine engines typically include a compressor for compressing air.The compressed air is mixed with a fuel and channeled to a combustor,wherein the fuel/air mixture is ignited within a combustion chamber togenerate hot combustion gases. The combustion gasses are channeled to aturbine, which extracts energy from the combustion gases for poweringthe compressor, as well as producing useful work. The exhaust gases arethen discharged through an exhaust nozzle, thus producing a reactive,propelling force.

Modern aircraft have increased hydraulic and electrical loads. Anelectrical load demanded of gas turbine engines increases as flightcomputers, communication equipment, navigation equipment, radars,environmental control systems, advanced weapon systems, and defensivesystems are coupled to aircraft. A hydraulic load demanded of gasturbine engines increases as flight controls, pumps, actuators, andother accessories are coupled to the aircraft. Within at least someknown aircraft, mechanical shaft power is used to power hydraulic pumps,electrical generators and alternators. More specifically, electrical andhydraulic equipment are typically coupled to an accessory gearbox thatis driven by a shaft coupled to the turbine. When additional electricalpower or hydraulic power is required, additional fuel is added to thecombustor until a predefined maximum temperature and/or power operatinglevel is reached.

Because the density of air decreases as the altitude is increased, whenthe aircraft is operated at higher altitudes, the engine must workharder to produce the same shaft power that the engine is capable ofproducing at lower altitudes. As a result of the increased work, theturbine may operate with increased operating temperatures, such that theshaft power must be limited or reduced to prevent exceeding the enginepredefined operating limits.

Within at least some known gas turbine engines, electrical power andhydraulic power is also generated by an auxiliary power unit (APU). AnAPU is a small turbo-shaft engine that is operated independently fromthe gas turbine engines that supply thrust for the aircraft. Morespecifically, because APU operation is also impacted by the air densityand is also operationally limited by predefined temperature andperformance limits, APUs are typically only operated when the aircraftis on the ground, or in emergency situations while the aircraft is inflight.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for assembling a gas turbine engine assembly isprovided. The method comprises providing at least one propelling gasturbine engine that includes a core engine including at least oneturbine, coupling an auxiliary engine to the propelling gas turbineengine such that during operation of the propelling gas turbine engine,such that at least a portion of the airflow entering the propelling gasturbine engine is extracted from the propelling gas and channeled to theauxiliary engine for generating power, and coupling a modulating valvein flow communication to the propelling gas turbine engine to controlthe flow of airflow from the propelling gas turbine engine to theauxiliary engine, wherein the modulating valve is selectively operableto control an extraction point of airflow from the propelling gasturbine engine.

In another aspect, a gas turbine engine assembly is provided. The gasturbine engine assembly includes at least one propelling gas turbineengine, a modulating valve, and an auxiliary engine used for generatingpower. The propelling gas turbine engine includes a fan, a core enginedownstream from the fan, and a plurality of extraction points. Themodulating valve is coupled in flow communication to each propelling gasturbine engine. The auxiliary engine includes at least one turbine andan inlet. The inlet is coupled in flow communication with the modulatingvalve, such that a portion of airflow entering the propelling engine isextracted for use by the auxiliary engine and such that the modulatingvalve controls the flow of airflow from the propelling engine to theauxiliary engine. The modulating valve is selectively operable toextract airflow from at least two of the plurality of extraction points.

In a further aspect, an aircraft gas turbine engine assembly including apropelling gas turbine engine, a modulating valve, and at least oneauxiliary engine is provided. The propelling gas turbine engine includesa core engine and an exhaust. The core engine includes at least oneturbine, and the propelling gas turbine engine is used for generatingthrust for the aircraft. The modulating valve is coupled in flowcommunication with at least one of a plurality of airflow extractionsources defined within the propelling gas turbine engine. The auxiliaryengine includes an inlet, at least one turbine, and an exhaust. Theinlet is coupled in flow communication with the modulating valve suchthat a portion of airflow flowing through the propelling engine isselectively extractable from the at least one propelling engine and ischanneled to the auxiliary engine for generating power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary schematic view of a gas turbine engine assembly.

FIG. 2 is a partial schematic view of an alternative embodiment of thegas turbine engine assembly shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an exemplary schematic view of a gas turbine engine assembly10 including a propelling gas turbine engine 11 and an auxiliary powerunit or auxiliary power engine 12 that are coupled together, asdescribed in more detail below, in a combined cycle. More specifically,gas turbine engine assembly 10, as described in more detail below,facilitates producing shaft power and propelling force for an aircraft(not shown).

Gas turbine engine 11 includes a core engine 13 and a fan assembly 14and a low pressure turbine assembly 20. Core engine 13 includes ahigh-pressure compressor 16, a combustor (not shown), and ahigh-pressure turbine 18. Fan assembly 14 and turbine 20 are coupled bya first shaft 22, and compressor 16 and turbine 18 are coupled by asecond shaft 23. Gas turbine engine 11 also includes an inlet side 24and an exhaust side 26. In one embodiment, engine 11 is a F118-GE-100turbofan engine commercially available from General Electric AircraftEngines, Cincinnati, Ohio.

In operation, inlet air, represented by arrow 30, enters fan assembly14, wherein the air is compressed and is discharged downstream,represented by arrow 31, at an increased pressure and temperaturetowards core engine 13 and more specifically, towards high-pressurecompressor 16. In one embodiment, engine 11 includes a bypass duct (notshown) such that a portion of air 31 discharged from fan assembly 14 isalso channeled into the bypass duct rather than entering core engine 13.

Highly compressed air 35 is delivered to a combustor (not shown) whereinit is mixed with fuel and ignited. Combustion gases propel turbines 18and 20, which drive compressor 16 and fan assembly 14, respectively. Inthe exemplary embodiment, core engine exhaust 32 is discharged fromengine to generate a propelling force from gas turbine engine assembly10. In the exemplary embodiment, core engine exhaust 32 is channeled toa variable area bypass injector 82 that is coupled in flow communicationwith core engine exhaust 32 and auxiliary engine exhaust 80. In analternative embodiment, core engine exhaust 32 is channeled to a mixingdamper (not shown) that is coupled in flow communication with coreengine exhaust 32. In another alternative embodiment, core engineexhaust flow and fan air are discharged separately from auxiliary engineexhaust 80 to produce thrust.

Auxiliary power engine 12 is coupled in flow communication to engine 11,as described in more detail below, and includes a compressor 42, ahigh-pressure turbine 44, and a low-pressure turbine 46. Compressor 42and high-pressure turbine 44 are connected by a first shaft 43 such thatas combustion gases propel turbine 44, turbine 44 drives compressor 42.Auxiliary engine 12 also includes a second shaft 48 coupled tolow-pressure turbine 46 which provides shaft power output, representedby arrow 49, for use in the aircraft. Power output 49 may be used todrive equipment, such as, but not limited to alternators, generators,and/or hydraulic pumps. In one embodiment, auxiliary power engine 12 isa turbo-shaft engine, such as a T700-GE-701 engine that is commerciallyavailable from General Electric Company, Cincinnati, Ohio, and that hasbeen modified in accordance with the present invention.

Auxiliary ducting (not shown) couples auxiliary power engine 12 toengine 11 to enable a portion of air 31 channeled towards core engine 13to be directed to auxiliary power engine 12. More specifically,auxiliary airflow, represented by arrow 52 is extracted from core engine13 at a location upstream from core engine turbine 18. In the exemplaryembodiment, airflow 52 is bled from high-pressure compressor 16 and isrouted towards auxiliary engine compressor 42. In an alternativeembodiment, auxiliary power engine 12 is coupled in flow communicationto a pair of engines 11 and receives high pressure airflow 54 from eachengine 11. In another alternative embodiment, a pair of auxiliary powerengines 12 are coupled in flow communication to a single engine 11 andboth receive high pressure airflow 54 from engine 11. More specifically,in the exemplary embodiment, compressor 16 is a multi-staged compressorand air 52 may be extracted at any compressor stage based on pressure,temperature, and flow requirements of auxiliary engine 12. In anotherembodiment, air 52 is extracted downstream from compressor 16. In afurther alternative embodiment, air 52 is extracted upstream fromcompressor 16. In one embodiment, approximately up to 10%, or more, ofair flowing into compressor 16 is extracted for use by auxiliary engine12. In a further embodiment, air 52 is extracted from any of, but is notlimited to being extracted from, a booster interstage, a boosterdischarge, a fan interstage, a fan discharge, a compressor inlet, acompressor interstage, or a compressor discharge bleed port. In anotherembodiment, approximately up to 10% or more, of air flowing into fan 14is extracted for used by auxiliary engine 12.

In an alternative embodiment, engine 11 supplies pressurized orcompressed air to auxiliary power engine 12. For example, in oneembodiment, compressed air supplied to an aircraft cabin is routed toauxiliary power engine 12 after being used within the aircraftenvironmental control system. In a further embodiment, auxiliary powerengine 12 receives a mixture of airflow from engine 11 and ambientairflow.

Auxiliary airflow 54 directed towards auxiliary engine 12 is at a higherpressure and temperature than airflow 30 entering gas turbine engineassembly 10. Moreover, because the auxiliary airflow 30 is at anincreased pressure and temperature than that entering gas turbine engineassembly 10, a density of airflow 54 is substantially similar to thedensity of airflow that enters auxiliary engine 12 at lower altitudes.Accordingly, because the power output of auxiliary engine 12 isproportional to the density of the inlet air, during operation of coreengine 13, auxiliary engine 12 is operable at higher altitudes withsubstantially the same operating and performance characteristics thatare available at lower altitudes by auxiliary engine 12. For example,when used with the F110/F118 family of engines, auxiliary engine 12produces approximately the same horsepower and operating characteristicsat an altitude of 30-40,000 feet, as would be obtainable if auxiliaryengine 12 was operating at sea level independently. Accordingly, atmission altitude, a relatively small amount of high-pressure air takenfrom core engine 13 will enable auxiliary power engine 12 to outputpower levels similar to those similar from auxiliary power engine 12 atsea level operation.

In the exemplary embodiment, auxiliary airflow 52 is channeled throughan intercooler 60 prior to being supplied to auxiliary engine compressor42. Intercooler 60 has two airflows (not shown) in thermal communicationwith each other and is designed to exchange a substantial amount ofenergy as heat, with minimum pressure losses. In the exemplaryembodiment, auxiliary airflow 52 is the heat source and a second airflowis used as a heat sink. In one embodiment, the second airflow is fandischarge airflow. In another embodiment, the second airflow is ambientairflow routed through an engine nacelle and passing through intercooler60 prior to being discharged overboard. More specifically, the operatingtemperature of auxiliary airflow 54 is facilitated to be reduced withinintercooler 60 as the transfer of heat increases the temperature of theother airflow channeled through intercooler 60. In an alternativeembodiment, turbine engine assembly 10 does not include intercooler 60.

Intercooler 60 facilitates increasing an amount of power per pound ofbleed air 54 supplied to auxiliary power engine 12 without increasingflow rates or changing existing turbine hardware. A control system 62 iscoupled to a generator control system (not shown) and facilitatesregulating the operating speed of auxiliary power engine 12. In oneembodiment, control system 62 throttles inlet air 52 supplied to engine12 by control of a variable flow area throttle valve 61 and/or controlsengine backpressure by control of a variable flow area exit nozzle 63 ora variable area bypass injector 82 to facilitate controlling theoperation of auxiliary power engine 12.

Exhaust airflow 80 from auxiliary power engine 12 is channeled towardscore engine exhaust 32 at a discharge pressure that is substantially thesame as a discharge pressure of exhaust flow 32 discharged from coreengine 13. Specifically, in the exemplary embodiment, auxiliary engineexhaust airflow 80 is routed through a variable area bypass injector 82which facilitates mixing exhaust flow 32 exiting core engine 13 withauxiliary engine exhaust airflow 80. More specifically, in the exemplaryembodiment, exhaust airflow 80 is reintroduced to core engine exhaustflow 32 upstream from a propelling core engine nozzle (not shown). Themixed exhaust flow 86 is then discharged through an engine nozzle (notshown). In an alternative embodiment, exhaust airflow 80 is not mixedwith core engine exhaust flow 32, but rather is discharged independentlyfrom exhaust flow 32.

Accordingly, when operated, auxiliary power engine 12 facilitatesproviding increased shaft power production for use within the aircraft.More specifically, because auxiliary power engine 12 is selectivelyoperable for shaft power production, auxiliary power engine 12 may beused only when needed, thus facilitating fuel conservation for theaircraft. In addition, the design of gas turbine assembly 10 enablesauxiliary power engine 12 to be operated independently of propellingengine 11, such that an operating speed auxiliary power engine 12 isindependent of an operating speed of core engine 13. As such, auxiliarypower engine 12 may operated during non-operational periods of coreengine 13, and moreover, may be used to provide power necessary to startoperation of engine 11.

Operation of auxiliary power engine 12 facilitates improving surgemargin of engine 11 by bleeding airflow 52 as needed, such thataltitude, installation, or distortion effects may be overcome. Moreover,by removing high pressure extraction, auxiliary power engine 12 alsofacilitates improving an operating performance of core engine 13 whilegenerating significant power. Additionally the hydro mechanical ordigital controls of propelling engine 11 and auxiliary power engine 12are arranged to mutually exchange operational status and performanceparameter values (pressure, temperature, RPM, etc) from one to theother.

FIG. 2 is a partial schematic view of an alternative embodiment of gasturbine engine assembly 10. Specifically, the engine assembly shown inFIG. 2 is the same engine assembly shown in FIG. 1, with the exceptionof a few component changes, described in more detail below. As such,components shown in FIG. 2 that are identical to components illustratedin FIG. 1 are identified in FIG. 4 using the same reference numeralsused in FIG. 1. More specifically, in the embodiment illustrated in FIG.2, engine assembly 10 includes a control valve assembly 100 thatfacilitates controlling airflow 54 channeled towards auxiliary powerengine 12.

In the exemplary embodiment, control valve assembly 100 includes a pairof modulating or control valves 102 and 104 that are operatively coupledto control system 62. Specifically, in the exemplary embodiment, controlvalve 102 is known as a low pressure source control valve, and controlvalve 104 is known as a high pressure source control valve. Valves 102and 104 work in cooperation, as described in more detail below, tofacilitate controlling a temperature, density, and/or pressure ofauxiliary airflow 54 channeled to auxiliary power engine 12.

Control valve assembly 100 is coupled in flow communication betweenpropelling engine 11 and auxiliary power engine 12 such that airflow 54channeled to power engine 12 is routed through valve assembly 100. Inthe exemplary embodiment, a back-flow control device 106 is coupledbetween propelling engine 11 and low pressure source control valve 102to facilitate preventing back flow from control valve assembly 100towards propelling engine 11. In the exemplary embodiment, controldevice 106 is, but is not limited to being, a check valve assembly.Moreover, in the exemplary embodiment, control valve assembly 100 iscoupled in flow communication with propelling engine 11 such thatintercooler 60 is coupled in flow communication between propellingengine 11 and control valve 104.

As described above, control valve assembly 100 is operatively coupled tocontrol system 62 such that valve assembly 100, and more specifically,valves 102 and/or 104, are selectively operable to control airflow 54channeled to auxiliary power engine 12. Moreover, as described in moredetail below, during engine operation control system 62 facilitatescontrolling the extraction location of airflow 54, and thus facilitatescontrolling the pressure, density, and airflow 54 channeled to auxiliarypower engine 12. As such, control valve assembly 100 can be selectivelyadjusted to facilitate optimizing supply pressure, temperature, anddensity of airflow 54, thus facilitating minimizing performancepenalties associated with engine 12 and maximizing power output 49.

For example, during operation at low altitudes, control system 62 isoperable to ensure that auxiliary power engine 12 receives airflow 54from a low-pressure extraction source, such as, but not limited to fandischarge 31, such that airflow 54 flows through check valve 106 and lowpressure control valve 102 prior to being introduced to engine 12.During operation at high altitudes, control valve assembly 100 isadjusted to ensure that auxiliary power engine 12 receives airflow 54from a high-pressure extraction source, such as, but not limited tocompressor discharge 35, such that airflow 54 flows through intercooler60 and high pressure control valve 104 prior to being introduced toengine 12. During operation at intermediate altitudes, auxiliary powerengine 12 receives airflow 54 at an intermediate pressure such thatairflow is blended from high- and low-pressure extraction sourcesthrough valves 102 and 104.

Control system 62 facilitates controlling control valve assembly 100 toenable auxiliary power engine 12 to receive a low pressure/lowtemperature/low density airflow, a high pressure/high temperature/highdensity airflow, or an intermediate pressure/intermediatetemperature/intermediate density airflow, based on several factorsand/or engine operating characteristics. In one embodiment, such factorsmay include, but are not limited to including, auxiliary engineoperability, demand for auxiliary engine power, propelling engineoperability, and/or propelling engine efficiency.

When it is desired to operate auxiliary power engine 12 with a source oflow pressure/low temperature/low density airflow, such airflow 122 maybe extracted from a plurality of different extraction points withinpropelling engine 11. For example, fan 14 is a multi-staged compressorand fan interstage bleed air 124 may be extracted from any fan stagebased on pressure, temperature, and flow requirements of auxiliaryengine 12. Moreover, such airflow may be extracted from any locationdownstream from fan 14 as booster discharge air, booster inter-stagebleed air, or core drive fan discharge air. Other alternative extractionsources for such airflow may include, but are not limited to including,fan discharge air 31 or fan inter-stage bleed air 124. Furthermore, inanother alternative embodiment, ambient air 30 may be used as a sourceof low pressure/low temperature/low density airflow.

When it is desired to operate auxiliary power engine 12 with a source ofhigh pressure/high temperature/high density airflow, such airflow 52 maybe extracted from a plurality of different extraction points withinpropelling engine 11. For example, as previously described, compressorinterstage bleed air 120 may be extracted from any compressor stagebased on pressure, temperature, and flow requirements of auxiliaryengine 12. Moreover, such airflow may be extracted at any locationupstream from compressor 16 as booster discharge air, boosterinter-stage bleed air, or core drive fan discharge air.

Control valve assembly 100 increases an operating flexibility ofauxiliary power engine 12 and an overall efficiency of gas turbineengine assembly 11. Specifically, control valve assembly 100 enablesauxiliary power engine 12 to be operated independently of propellingengine 11. Moreover, because valves 102 and 104 are selectivelyoperable, airflow to auxiliary power engine 12 may be adjusted tofacilitate optimizing supply pressure, temperature, and density, thusminimizing performance penalties and maximizing power output 49. Inaddition, the selective operation of control valve assembly 100 enableslow pressure air, at a lower performance penalty, to be used at lowaltitudes or when a reduced amount of auxiliary power output 49 isrequired, and enables high pressure air to be used at higher altitudesor when increased power output 49 is demanded. Furthermore, auxiliaryengine air supply can also be selectively adjusted in cooperation withpropelling engine inlet guide vanes, variable geometry, and a variablebypass injector 82, to facilitate increasing stall margin, improvingoperability, and to facilitate reducing performance penalties and fuelburns.

The above-described modulating control valve assembly is cost-effectiveand facilitates increases shaft power production and turbine engineoperating efficiency. The control valve assembly is coupled in flowcommunication between the propelling engine and the auxiliary engine tofacilitate enhanced operation and control of airflow channeled to theauxiliary power engine. As such, the control valve assembly may beselectively adjusted to facilitate a small amount of high-pressure airtaken from the main engine to enable a smaller engine to output powerlevels similar to those of sea level operation. As a result, theincreased control of airflow directed to the auxiliary enginefacilitates increased turbine power production from the auxiliary enginein a cost-effective and reliable manner.

Exemplary embodiments of gas turbine assemblies are described above indetail. The assemblies are not limited to the specific embodimentsdescribed herein, but rather, components of each assembly may beutilized independently and separately from other components describedherein. For example, each turbine component and/or auxiliary turbineengine component can also be used in combination with other core engineand auxiliary turbine engine components.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A gas turbine engine assembly comprising: at least one propelling gasturbine engine comprising a fan, a core engine downstream from the fan,and a plurality of extraction points; a modulating valve coupled in flowcommunication to said at least one propelling gas turbine engine; and anauxiliary engine used for generating electrical power, said auxiliaryengine comprising at least one turbine and an inlet, said inlet coupledin flow communication with said modulating valve, such that a portion ofairflow entering said at least one propelling engine is extracted foruse by said auxiliary engine and such that said modulating valvecontrols the flow of airflow from said at least one propelling engine tosaid auxiliary engine, said modulating valve is selectively operable toextract and mix airflow from at least two of said plurality ofextraction points.
 2. A gas turbine engine assembly in accordance withclaim 1 wherein said modulating valve is coupled to a first of saidplurality of extraction points for selectively controlling a flow ofhigh-pressure airflow to said auxiliary engine and to a second of saidplurality of extraction points for selectively controlling a flow oflow-pressure airflow to said auxiliary engine.
 3. A gas turbine engineassembly in accordance with claim 1 wherein said modulating valve isselectively operable to facilitate controlling at least one of apressure, a temperature, and a density of airflow channeled to saidauxiliary engine.
 4. A gas turbine engine assembly in accordance withclaim 1 wherein said modulating valve is selectively operable tofacilitate increasing at least one of a stall margin and an operabilityof said propelling gas turbine engine.
 5. A gas turbine engine assemblyin accordance with claim 1 wherein said modulating valve is selectivelyoperable to facilitate increasing an operating efficiency of saidpropelling gas turbine engine.
 6. A gas turbine engine assembly inaccordance with claim 1 wherein said modulating valve is coupled to atleast two of said extraction points such that during at least someengine operations, said auxiliary engine receives airflow from at leastone extrication point coupled in flow communication with a high-pressuresource of air and from an extrication point coupled in flowcommunication with a low-pressure source of air.
 7. A gas turbine engineassembly in accordance with claim 1 wherein said modulating valvefacilitates said auxiliary engine generating increased shaft horsepowerduring operation of said gas turbine engine assembly.
 8. An aircraft gasturbine engine assembly, said assembly comprising; at least onepropelling gas turbine engine comprising a core engine and an exhaust,said core engine comprising at least one turbine, said at least onepropelling gas turbine engine for generating thrust for the aircraft; amodulating valve coupled in flow communication with at least one of aplurality of airflow extraction points defined within said at least onepropelling gas turbine engine, said modulating valve is selectivelyoperable to extract and mix airflow from at least two of said pluralityof airflow extraction points; and at least one auxiliary enginecomprising an inlet, at least one turbine, and an exhaust, said inletcoupled in flow communication with said modulating valve such that aportion of airflow flowing through said propelling engine is selectivelyextractable from said at least one propelling engine and is channeled tosaid auxiliary engine for generating electrical power.
 9. An aircraftgas turbine engine assembly in accordance with claim 8 wherein saidmodulating valve is selectively operable to facilitate controlling atleast one of a pressure, a temperature, and a density of airflowextracted from said at least one propelling engine and channeled to saidat least one auxiliary engine.
 10. An aircraft gas turbine engineassembly in accordance with claim 8 wherein said at least one auxiliaryengine is operable independently of said at least one propelling gasturbine engine.
 11. An aircraft gas turbine engine assembly inaccordance with claim 8 wherein said modulating valve facilitates saidauxiliary engine generating increased shaft horsepower during operationof said gas turbine engine assembly.
 12. An aircraft gas turbine engineassembly in accordance with claim 8 wherein operation of said modulatingvalve facilitates enhancing at least one of a stall margin and theoperability of said at least one propelling engine.
 13. An aircraft gasturbine engine assembly in accordance with claim 8 wherein operation ofsaid modulating valve facilitates improving operating performance ofsaid at least one propelling engine, said modulating valve is coupled toat least two of said airflow extraction points such that during at leastsome engine operations, said auxiliary engine receives airflow from atleast one extrication point coupled in flow communication with ahigh-pressure source of air and from at least one extrication pointcoupled in flow communication with a low-pressure source of air.